Re: Studiomaster Powerhouse Vision 8 , 700W mixer amp,1996

glad to see we are not alone got similar problem,have run studiomaster
vision 8 for 12months no prob but have suspected fan not doing its
stuff. summertime is hot here so used external fan just to be
sure,However--- big prob occured running just one guitar in practice
session, unit suddenly lost digital display, developed loud squeal
from both speakers, master straight to off, peak red lights showing
max!! then nothing.
tried powering up again same result.
have carried out detailed inspection, all pcb's ok visually.ribbon
cables and pins good,transformer seems ok but I'm not sure what value
outputs I should be measuring at each pin??
would really appreiciate any help

I've not got the schematic but I've found you can run it stripped down.
Disconnect the 2 pa and all the ribbon cables except the one between the ps
one, via small rear panel and up to the mixer. To check for any mixer
problems, removing display and memory stuff, monitor output by phones.
It looks, not done so yet, that you can then plug in one amp at a time , or
swap around , to localise single channel problem to one ch or the other in
pa or mixer section.
There seems to be odd power rails , +/65V main power rails and a pair of
+/79V.
I have some monitored voltages at the pa headers, will get back to it today

 

With pa's and mixer removed and Conn3 and conn4 ribbons removed, so just the
main combined ps and thermal board in place, DC voltages on con3
80,0.2(£),15,0,0
-80,16.6($),0,0,0 (*)

* has 0.6V ac, and £ has 0.2Vac on it with 400Hz input and 0db bar
registered on the meter
$, 16.6V via 100R to base of thermal monitor TO220 ,to test point T12 ,
obviously drops down to Vbe , with pa in place

T10 for the other amp TP

The 0.6V ac also on that pin of conn4, clear and balanced , unlike
originally with all connected, very marked signal imbalance. There was a
problem with the "group" slider , but maybe not the cause of original
problem. I will next try with swapped pas in place, then display board if
all seems well.

 

Previous 2x5 header volts viewed/monitored at pins , starting from main caps
end

At 75 percent or less of mains voltage both red LED "fault" lights light,
gives some sort of check of functioning.
I don't know what temperature is required to activate the yellow LEDs and
channel/channels ? shutdown, but presumably greater than 90 deg c

With PAs loose(on nylon standoff only, not nutted down) in the amp , make
sure there is insulation between both sets of live heatsinks.
You can monitor signal in of the PA at R11 , R9 end.
Monitoring output and T12 TP, increasing the heatsink temp with hot air gun
and fan off. No change in output level up to 90 deg C.
With fan connected , fan comes on (at T12) with Vbe between 0.61 and 0.62
and temp between about 45 and 55 degree C (the "thermal" Tr is underneath),
dropping to 0.52 or so at 90 deg C. Both channels checked like this